Volume Shadow Copy Service (VSS) writer updates in Windows Server 2008 and Vista SP1

[FileCAB-Team]

First published on TECHNET on Mar 03, 2008

For Server 2008 the VSS team invested a great deal in hardware shadow copy scenarios which you can read about here . Additionally significant work went into enhancing the APIs for writers and widening their adoption by other applications and components. Consequently Server 2008 has several new VSS writers for Windows components which aids in System State backups. In this post I'll touch on some of the API changes and the more notable writers. You can find more on VSS writers and the gory details of what they do during backups and restores on MSDN.

Concurrent backups and restores : With Windows Server 2008 it is possible to perform as many as 64 backup sessions and one restore session concurrently with a given writer. Previously only 8 concurrent backup sessions were possible and restores could not be performed simultaneously with backups. We expect applications with large numbers of stores to leverage this feature to shrink backup windows.

Exchange backups and restores are a very typical example where this helps. An Exchange server may have as many as 50 storage groups all of which are backed up independently. A restore of a user’s mailbox involves a restore to a recovery storage group which in the past would disrupt the routine backups.

In fact it's no co-incidence that the first writer to take advantage of this feature is Exchange 2007 SP1. The work in VSS was also back ported to Windows Server 2003 and is available with SP2.

To enable this functionality writers must indicate they support concurrent backups and restores with the backup schema flag VSS_BS_WRITER_SUPPORTS_PARALLEL_RESTORES . Writers must also be capable of managing state between multiple backup and restore sessions.

System state writers

System state writers assist with backing up and restoring the operating system, drivers and services. There may be several such writers on the system depending on the roles and features that are installed. The Registry and COM+ writers are a few of the constants while the Cluster Service and Active Directory are examples of writers that are available only when specific features or roles are installed.

All the inbox system state writers in Vista are also available in Vista SP1 and Server 2008. In addition Window Server 2008 has several writers that are listed here . You can examine the writers and their metadata using the Diskshadow command - list writers metadata.

New or updated writers : The writers that are all new for Server 2008 or that have changed significantly since Server 2003 include Cluster Services, IIS, ASR , Hyper-V, Windows Deployment Service, Terminal Services and the Network Policy Server. The IIS writer is also available for Vista beginning with SP1.

The System writer in Vista SP1 and Server 2008 now reports the .Net framework for backups. This was not the case in Vista.

Deprecated writers: The Remote Storage, MSDE and Event log writers have been dropped from Server 2008 and Vista. SQL 2005 SP2 is the first version of SQL to support Server 2008 and Vista and the SQL writer replaces the MSDE writer for SQL and wYukon backups.

In place backup and restores : One significant change from Server 2003 is that all the system state writers support in place backup and restores - this is true of both Vista and Server 2008. Previously some writers (Registry, COM+ and Clusters for example) required the backup to be performed from a spit or alternate location i.e. the writer would dump a copy of the data it protected to an alternate location for the backup and during the restore the data had to be placed back correctly. The differences in location caused additional complexity for backup applications which is no longer the case.

Most backup applications including Windows Server Backup leverage VSS and the inbox system state writers to perform system state backups and restores.

Application Writers

Since Server 2003 we’ve also worked with several applications within and outside Microsoft to help develop backup capabilities based on VSS writers. Some of the more recent additions to the fold include Systems Management Server (SMS), Sharepoint, Internet Security and Acceleration Server (ISA), Virtual Server, Commerce Server, Oracle 11G, and Microsoft Operations Manager (MOM).

You can expect to see a few more writers RTM this year. A few years ago the list used to be smaller and consisted of Exchange and SQL in addition to the inbox writers. As the ecosystem grows it’s getting harder to keep tabs on all of them. If you happen to spot a writer in the wild :) drop us a line at vss(nospam)@microsoft.com or leave a comment.

Dinesh